Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761727AbZDQQOj (ORCPT ); Fri, 17 Apr 2009 12:14:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758368AbZDQQO3 (ORCPT ); Fri, 17 Apr 2009 12:14:29 -0400 Received: from gw.goop.org ([64.81.55.164]:43620 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760918AbZDQQO2 (ORCPT ); Fri, 17 Apr 2009 12:14:28 -0400 Message-ID: <49E8AAE3.9060005@goop.org> Date: Fri, 17 Apr 2009 09:14:27 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Mathieu Desnoyers CC: Steven Rostedt , Ingo Molnar , linux-kernel@vger.kernel.org, "Paul E. McKenney" , Andrew Morton , Christoph Hellwig Subject: Re: [patch 2/3] RCU move trace defines to rcupdate_types.h References: <20090417003755.276959950@polymtl.ca> <20090417003931.846405986@polymtl.ca> <49E7D701.9090407@goop.org> <20090417014209.GA24956@Krystal> <49E81A63.7010700@goop.org> <20090417151646.GB13842@Krystal> <49E89FC1.70006@goop.org> <20090417154228.GB15046@Krystal> In-Reply-To: <20090417154228.GB15046@Krystal> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2371 Lines: 59 Mathieu Desnoyers wrote: > * Jeremy Fitzhardinge (jeremy@goop.org) wrote: > >> Mathieu Desnoyers wrote: >> >>> Given the simplicity of the preempt_disable/enable_notrace found in >>> preempt.h, we could move them to >>> >>> include/preempt_types.h too, and that would solve all problems, wouldn't >>> it ? >>> >>> >> No, it still needs linux/thread_info.h -> asm/thread_info.h, which in >> turn gets quite a lot of things on x86 (and would need to be audited in >> each architecture). >> >> J >> > > Well, I think it's a good time to do some cleanup then. Why on earth > would thread_info.h be anything else than a "_types"-like header ? > Why indeed? Because it includes a number of other headers to get the definitions it needs, and defines various functions needed to operate on the thread_info structure (including the all-important current_thread_info()). Yes, it can be refactored into thread_info.h and thread_info_types.h, and all the headers it includes can be similarly refactored, and linux/thread_info.h can also be split, and all the asm/*/thread_info.hs can be split too, and it can be made to work for all arches under all configs... But that's going to take a long time, and if its a pre-requisite for getting tracing going, then we're not going to see it merged this year. > If headers has become in such a state in the kernel, then IMHO the > solution is not to shove more out-of-line functions under the carpet, > but rather to do the cleanup. > Besides, I'm still not convinced that putting the code inline is a good idea. Direct call/return are not inherently expensive, and they're something that CPU vendors have a lot of motivation to optimise for. In particular, the call itself is no more expensive than a jmp other than the return-address push, and the ret is also cheap because it will use the return address cache rather than having to be a full indirect jmp. And it would be much easier to justify leaving tracing compile-time enabled all the time if each tracepoint really does have a minimal icache profile when not enabled. J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/